Transistors are key components of modern integrated circuits. To satisfy the requirements of increasingly faster speed, the drive currents of transistors need to be increasingly greater. To achieve this increase in performance, the gate lengths of transistors are constantly being scaled down. Scaling down the gate lengths, however, leads to undesirable effects known as “short-channel effects,” in which the control of current flow by the gates is compromised. Among the short-channel effects are the Drain-Induced Barrier Lowering (DIBL) and the degradation of sub-threshold slope, both of which resulting in the degradation in the performance of transistors.
The use of a multi-gate transistor architecture may help the relief of short-channel effects. Fin Field-Effect Transistors (FinFET) were thus developed. FinFETs have increased channel widths. The increase in the channel widths is achieved by forming channels that include portions on the sidewalls of semiconductor fins and portions on the top surfaces of the semiconductor fins. Since the drive currents of transistors are proportional to the channel widths, the drive currents of the FinFETs are increased.
In existing FinFET formation processes, Shallow Trench Isolation (STI) regions are first formed in a silicon substrate. The STI regions are then recessed to form silicon fins, which are the portions of the silicon substrate that are over the recessed STI regions. Next, a gate dielectric, a gate electrode, and source and drain regions are formed to finish the formation of the FinFET. Each of the silicon fins may be used to form a FinFET, although one FinFET may include a plurality of parallel silicon fins. In the respective FinFET, the channel includes both the sidewalls and the top surfaces of the semiconductor fins, and hence the drive current of the FinFET is high with relative to the chip area used by the FinFET. Accordingly, FinFET is becoming a trend in recent generations of integrated circuits.